This invention relates to a method for operating a glass melting furnace having a melting portion and at least one processing or working tank positioned adjacent thereto, as well as to a glass melting furnace for carrying out such method and having a melting portion and at least one processing tank communicating therewith through a passage.
In the processing tanks of glass melting furnaces from which the glass is withdrawn manually, mechanically or by means of feeders, glass defects are caused depending on the type and quantity of withdrawal. Heretofore, such defects could not be eliminated.
In manual withdrawal using gathering irons, in discharge of spherical feeders or in drawing of the glass by vacuum, bubbles are inherently produced because of the relatively high viscosity of the glass within the processing tank where temperatures are normally between 1050.degree. and 1250.degree. C. At best, such bubbles can only be incompletely removed heretofore.
Another drawback, particularly with low volumes of withdrawal, and which also occurs in the discharge or withdrawal of glass using feeders, is a temperature inhomogeneity which is due to a greater amount of thermal energy being dissipated in the processing tank through the basin wall than is supplied by fresh glass from the melting tank. This means that the glass must normally be heated by means of burners. However, because heat emission takes place in a position different from the position of heat supply, temperature inhomogeneities are avoidable. Another interfering factor is observed in glasses containing volatile components, such as boron, lead or fluorine. Because of the open glass surface within the processing tank and heating by means of burners, these glass constituents are vaporized at the surface of the melt which means that the surface glass has a composition different from that of the bottom glass. This undesirably and inherently results in chemical inhomogeneity and striation. Naturally the effect of this depends on the volume discharged in relation to the open glass surface. In the case of varying discharges, the intensity of this effect thus decreases or increases, and it cannot be compensated for in such cases.
It has been proposed to eliminate these well-recognized drawbacks by means of agitation with the aid of agitators. However, only a partial solution to the problem can be realized in this fashion. Although improvement can be obtained in the case of temperature inhomogeneities by proper operation of the agitators, the stagnation of cold glass at the bottom cannot be avoided. Furthermore, in the case of bubble formation, agitation merely results in dispersion and size reduction of such bubbles, which then are more resistant to break-up via an increasing accumulation of bubbles which takes place with the lapse of time.